The invention relates to a focal plane shutter.
In a focal plane shutter, the shutter blinds which have run are wound or charged subsequent to the completion of an exposure, by utilizing shutter blind windng gears which are interlocked with a film winding operation, for example, to drive pinions which are associated with shutter blind winding drums. A conventional winding apparatus comprises pinions and gears which are normally maintained in meshing engagement with each other. However, this may present a problem in providing a high speed shutter operation because the gears represent a load on the shutter blinds as they run. A type of winding apparatus is available in which both the first and the second pinions are simultaneously driven. With this construction, if there happens to be an opening between the two blinds when the shutter blinds have come to a stop, the winding procedure is performed with the opening maintained between the two blinds, thus disadvantageously exposing the film chamber to a taking lens path.
There is another problem involved with the conventional construction of prior art focal plane shutters. A focal plane shutter is constructed such that an exposure value is determined by both a diaphragm aperture and a time delay between the running of the first and second shutter blinds which is determined by a photometric result. With a high speed operation or when the exposure period is very brief, the second blind starts to run soon after the first blind has started to run, thereby forming a slit of a width which is substantially reduced relative to the width of an image field. Light from an object being photographed is made to impinge upon a film surface while the slit travels across the film field. Consequently, the slit width must be maintained constant during the shutter operation in order to assure a uniform exposure. However, a conventional focal plane shutter is generally designed such that the second blind runs slightly faster than the first blind in order to improve the accuracy of the exposure period. In extreme instances, the second blind, which initiates running with a certain delay after the first blind has started to run, may catch up with the first blind, resulting in a closed shutter condition while the two blinds travel across the film field. In such instance, there will be no exposure at all or an insufficient exposure.